1. Field of the Invention
The present invention relates to a light shielding blade such as a shutter blade and an aperture blade for a camera, and a method of manufacturing the same. In particular, the present invention relates to an edge face treatment of the light shielding blade for the purpose of preventing a harmful reflection.
2. Description of the Prior Art
FIG. 5 is a process diagram, which shows a method of manufacturing a conventional focal-plane shutter blade. At first, a shutter blade 11 having a predetermined planner shape is punched out from an aluminum foil 0 in step of FIG. 5(A). Subsequently, in step of FIG. 5(B), an alumite treatment is applied to a major face 11S and an edge face 11E of the punched shutter blade 11. Finally, in step of FIG. 5(C), the shutter blades 11 are collected and piled up, and the aligned edge faces of the shutter blades 11 are spray-coated by a nozzle 60. This kind of edge face coating technique for the purpose of preventing a side reflection is disclosed, for example, in Japanese Patent Unexamined Publication Nos. 56-70536, 64-57247 and 3-12642.
FIG. 6 is a schematic partial cross sectional view, which shows another example of a conventional light shielding blade. Front and back surfaces of a base piece 2 constituting the light shielding blade are coated with a coating 3 provided with a lubricating performance and a reflection preventing performance. Further, an edge face portion of the light shielding blade is also coated with a coating 3E having a reflection preventing performance. The coating 3E in the edge face portion of this kind is provided for the purpose of preventing a flare phenomenon from being generated due to a reflection of incident light. In addition to the coating, a sand blasting method is known as a method of treating an edge face for the purpose of preventing a reflection.
As mentioned above, for the purpose of preventing the reflection on the edge face of the light shielding blade, the spray coating has been applied to the edge face portion. This spray coating treatment can be efficiently performed in a state where a multiplicity of shutter blades 11 are piled up as shown in FIG. 5(C). However, among the light shielding blades which are employed for the camera and the like, there is an aperture blade shown in FIG. 7 in addition to the shutter blade. This aperture blade 8 is particularly designed for a digital camera, in which an opening 8a having an inner diameter of 1 to 2 mm is formed in a center portion. Since an optical axis of a lens passes through the opening 8a at a time of exposure operation, it is important to suppress an edge face reflection for preventing the flare phenomenon. However, since the inner diameter of the opening 8a is narrow in a range between 1 and 2 mm, it is impossible to spray-coating the edge faces of the openings 8a in a state of piling up a multiplicity of aperture blades 8.
Accordingly, as shown in FIG. 8, it is necessary to adopt spray coating by means of a nozzle 60 after placing the aperture blades 8 one by one in a flat plane. At this time, since a warp is generated due to a hardening stress of the coating in the case of single face coating, it is impossible to assemble the warped blade 8 in a shutter of the camera. Thus, it is necessary to coat both faces of each blade piece, however, there is a problem that much labor is required to turn over each blade piece and thus a manufacturing cost is increased. Further, in accordance with a compact size of the camera in recent years, the light shielding blade itself tends to be made compact and thin, and the coating in a state of placing the blades in a flat plane as shown in FIG. 8 is difficult. Such handling of blade pieces is not an efficient working method.
In addition, there is a dip method in which a coating is formed by dipping the aperture blades 8 into a resin solution provided with a reflection preventing effect and by pulling up the blades 8 from the resin solution. However, in this dip method, since a thickness of a coating of an inner peripheral edge surface in the opening 8a becomes too great, the method cannot be actually used. Otherwise, it can be considered that a writing brush is employed and a coating material is manually applied to the inner peripheral surface of the opening 8a by the writing brush, however, there is a problem that a thickness thereof is individually fluctuated.
In order to solve the problems in the prior art mentioned above, there is provided the following means. That is, in accordance with the present invention, there is provided a method of manufacturing a light shielding blade having a major face portion capable of shielding a light and an edge face portion perpendicularly crossing the major face portion by using a base piece which is formed in a predetermined shape from a film material made of a polyester. The method comprises a punching step of punching the base piece from the film material in a predetermined shape, and a chemical etching step of applying a chemical etching onto an edge face portion of the punched base piece so as to roughen the edge face portion, thereby suppressing a light reflection on the edge face portion. In particular, the punching step is performed by punching the base piece in a predetermined shape from a film material provisionally oriented bi-axially and made of a polyethylene terephthalate, and the chemical etching step is performed by dipping the base piece for 5 to 20 minutes into an aqueous solution in which 20 to 50 wt % NaOH or KOH is dissolved and which is heated to 80 to 95xc2x0 C. In a preferable form, the punching step mentioned above is performed after provisionally forming a coating having at least one of an electric charge preventing effect, a lubricating effect and a frosting effect on a surface of the film material and having a chemical etching resist performance. The coated film material is punched in a predetermined shape to form the base pieces of the blades. Further, in accordance with the present invention, there is provided a light shielding blade having a flat major face portion capable of shielding a light and an edge face portion suppressing a light reflection by using a film material made of a polyester as a base piece, wherein the edge face portion is constituted by a porous surface layer obtained by roughening a cut surface of the base piece having a minute composition. The base piece is made of, for example, a bi-axially oriented polyethylene terephthalate.
It is possible to etch a polyethylene terephthalate (PET) by employing a sodium hydroxide (NaOH) or a potassium hydroxide (KOH). Conventionally, in the case of a PET film material or the like, the chemical etching is mainly used as a surface treatment on a major face in general. For example, this method is employed for a surface treatment (a preliminary treatment) before a bonding or adhesive operation. In accordance with the present invention, in contrast, roughening process of the edge face portion is performed while keeping a smooth state of the flat major face portion of the light shielding blade as it is, by applying a chemical etching to the edge face portion. At a time of roughening by the chemical etching, it is necessary to control a temperature, a concentration and a time of the etching solution to an optimum condition. As a result, it is possible to form pores having a diameter of about some xcexcm and being locally disposed only on a surface layer of the edge face portion. It is possible to suppress a mirror reflection, which would generate a flare phenomenon or the like, by making the edge face portion porous. In this case, by provisionally applying a coating, which is not corroded by an alkaline or which has a low etching speed, to the film material. Thereafter, the film material is punched into a shape of the light shielding blade, and the chemical etching treatment is applied to a cut surface of the punched blade piece. By such a manner, it is possible to roughen only the edge face portion while keeping a smooth state of the flat major face portion. Since the chemical etching is performed by a wet type treatment, not only an outer edge face of the light shielding blade but also an inner edge face such as an opening or the like can be easily roughened by dipping the blade pieces such that the inner edge face may be brought into contact with the etching solution, whereby the desired reflection preventing treatment can be performed. Since the light shielding blade such as the shutter blade, the aperture blade or the like is formed by punching the film or sheet material after provisionally forming the coating on the film surface, the coating can be used as a resist and it is possible to selectively roughen only the cut face which is exposed in accordance with the punching process.